hide result of formula until criteria is added

If I have 3 rows in col. A , with a formula in B3 "=A3+B1" A B C D E F G H I J

1. 75 202. 503. 30 50...and I add amount in B1 as 20, the result is going to be 50. NOW, I want to copy the same formula in B3 to the rest of the columns...C3,D3,E3, etc. BUT I don't want the total to show "50" in all the colums until I fill in the cells C1,D1,E1,F1, etc. Thanks!

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